He married Judi Dench on 5 February 1971, in the same year that they co-starred in a stage production of John Webster's The Duchess of Malfi. They had one daughter, Tara Cressida Williams (b. 1972), known as Finty Williams, who is also an actress. Finty has one offspring, son Sam Williams (b. 6 June 1997).[2]

Williams served as an enthusiastic supporter of the project to build the Blackfriars Playhouse in Staunton, Virginia, USA. A plaque commemorating Williams' contributions hangs in the completed playhouse.

Shortly before his death from lung cancer at the age of 65, Williams was appointed a Knight of St Gregory (KSG) by Pope John Paul II for his contribution to Catholic life in Britain. The honour was officially bestowed upon him at home on 10 January 2001. He died the next day.[4]